Method for stabilizing lubricating oil



States Patent METHOD FOR STABILIZING LUBRICATING OIL James Van Dy'clr Fear, Media, Pa., assignor to Sun Oil ompany, Philadelphia, Pa., a corporation of New f ersey 1 No'brawin r Application February 7, 1951 Serial N0. 638,690

2 Claims. (Cl. 208-264) This invention relates to a method for stabilizing acid treated lubricating oils, and more particularly to a method for stabilizing the unsulfonatable oil recovered from a process for the production of petroleum sulfonates.

In the production of petroleum sulfonates, it has been the practice to contact a solvent raffinate or other petroleum fraction of lubricating viscosity with fuming sulfuric acid, oleum, or anhydrous sulfur trioxide, in order to convert a major portion of the aromatics in the fraction to sulfonic acids. Acid sludge is separated from the sour oil, which is then treated with an alcoholic caustic solution to remove the sulfonic acids as sodium sulfonates. The oil recovered from the caustic treatment has a higher V.I. than the raffinate charged to the sulfonation process, and is apparently neutral.

The oil contains, however, in spite of its apparent neutrality, some sulfur compounds formed during the sulfonation treatment. These compounds, while unidentified, are believed to be oxygenated compounds such as sulfino, sulfinyl, or sulfonyl compounds which decompose, when the oil is subjected to moderately elevated temperature, such as those encountered in distillation, to highly acidic substances which are very corrosive to plant equipment. Such sulfur compounds are apparently quite different in composition from the naturally occurring petroleum sul-' fur compounds, since the latter do not exhibit this behavior.

In the past, a number of proposals have been made for treating such oils to eliminate the very serious corrosion problems posed by their potential acidity. As previously mentioned, treatment with a caustic solution eifects no improvement. If the oil is heated to a temperature at which the sulfur compounds will decompose, say from 400 F. to 700 F., and is then cooled and caustic treated,

some improvement is effected, but the oil on reheating to decomposition temperature may again become sour unless it is heated for a prolonged period of time. This treatment is quite expensive, and in addition, a sludge is formed during the heat treatment which must be removed to obtain an oil of acceptable color.

Another proposal for treating the oil has been to subject the oil to high temperatures while blowing the oil with an inert gas to remove volatile decomposition prod ucts as they are formed. If the heating and blowing are continued for a sufficient length of time, for example one hour at 600 F., the deleterious compounds can be substantially completely removed. During the treatment, black sludge is produced which represents a net loss of product, and which must be removed by redistillation or clay treatment, at an added expense.

It is an object of this invention to provide a continuous process for removing from an oil, acid-forming substances which have been introduced thereto in the course of treatment of the oil to produce petroleum sulfonates.

It is a further object of this invention to provide a process for stabilizing acid-treated oils which produces 2,908,638 Patented Oct. 13, 1959 2 an oil of acceptable color without the need of subsequent treatment teimprove eelor. I I

It a still further object 'of this invention to provide a process for stabilizing acid treated oils in which the 'V.I.,ofthe finished oil is not adversely affected.

In accordance with the present invention I have found that the foregoingobjects ma be attained by hydrogenating an oil containing acidic precursors picked up during sulfonation in liquid phase, and in the presence of a sulfur-resistant hydrogenation catalyst, under mild conditions which preclude dehydrogenation of naphthenes to aromatics. Process conditions include a pressure of from about p.s.i.g. to about 300 p.s.i.g., temperature of from about 450 F. to about 700 F., and liquid hourly space velocity (volume of charge/volume of catalyst bed) of from 0.5 to 5. Any sulfur-resistant hydrogenation catalyst known to the art may be used, but molybdenum sulfide or tungsten sulfide are the preferred catalysts. Pressures higher than 300 p.s.i.g. may be used, but are not required, and are not preferred, since the cost of equipment rises rapidly with rising process pressures, and at higher pressures some hydrocracking of the oil may occur. Since the temperature does not exceed about 700 F., there is no danger of dehydrogenation of naphthenes at the low pressures used. It would appear that the sulfur compounds introduced into the oil by the sulfonation treatment are much less resistant to hydrogenation than sulfur compounds Occurring naturally in petroleum oils, since the conditions employed in the present process would have little, if any, eifect if used to treat a petroleum distillate of lubricating viscosity to reduce its natural sulfur content.

As an example of the results obtained when proceeding according to the present invention in a commercial operation, a solvent-extracted rafiinate of lubricating viscosity containing about 12% aromatic compounds was treated with anhydrous sulfur trioxide in the amount of about 24 pounds per barrel of oil at a temperature of F. The sulfonation products were then stripped with air to remove unreacted sulfur trioxide, together with any sulfur dioxide formed in the reaction, and were settled to separate a sour oil layer and a sludge layer. The sour oil layer Was removed, and was mixed with an equal volume of aviation alkylate in order to reduce its viscosity. This mixture was then contacted with an alcoholic caustic solution in an amount in excess of that required to neutralize the sulfonic acids contained in the sour oil, and an upper oil layer complising alkylate and unsulfonatable oil was recovered. The alkylate was separated from the unsulfonatable oil by distillation to yield as bottoms a lubricating oil containing about 0.09% sulfur by weight. This oil appeared to be neutral, and was of good color, but, when heated to 600 F. during further processing, it became extremely corrosive, in spite of its low sulfur content, and rapidly darkened to an unacceptable color.

A sample of the oil, as recovered from the alkylate separation step was passed into contact, in liquid phase,

with a molybdenum disulfide catalyst, under a hydrogen pressure of '150 p.s.i.g. at a temperature of 550 F., and at a liquid hourly space velocity of 1. The product recovered, when freed of gaseous products including dissolved hydrogen, contained 0.02% sulfur and was found to be completely color-stable and non-corrosive even after exposure to temperatures in excess of 600 F. Apparently the sulfur remaining in the oil was naturallyoccurring sulfur which remained in the oil after the treatment with sulfur trioxide, since heat treatment did not break down the compounds containing the residual sulfur into acidic substances. No dark-colored compounds were formed during the hydrogenation treatment, and

. V a. 3 v no further refining was necessary to produce a stable lubricating oil of acceptable color.

I claim:

1. A process for the production of stable oils-ofvlubricating viscosity which comprises treating a petroleum fraction of lubricating viscosity with anhydrousrsulfur trioxide, whereby to form sulfonic acids, separating sulfom'c acids from the treated petroleum fraction, contacting the treated fraction with hydrogen, in the presence of a sulfur resistant hydrogenation catalyst, at apressure of from about 150 p.s.i.g. to about 300 p.s.i.g-. and at a temperature of from about 450 F. to about 700 F., but below the temperature at which appreciable dehydrogenation of naphthenes to aromatics or hydrocracking will take place at the pressure used, and recovering an oil which will not discolor on heating to a temperature in excess of 400 F.

2. The process according to claim 1 in which the hydrogenation catalyst is molybdenum disulfide.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A PROCESS FOR THE PRODUCTION OF STABLE OILS OF LUBRICATING VISCOSITY WHICH COMPRISES TREATING A PETROLEUM FRACTION OF LUBRICATING VISCOSITY WITH ANHYDROUS SULFUR TRIOXIDE, WHEREBY TO FORM SULFONIC ACIDS, SEPARATING SULFONIC ACIDS FROM THE TREATED PETROLEUM FRACTION, CONTACTING THE TREATED FRACTION WITH HYDROGEN, IN THE PRESENCE OF A SULFUR RESISTANT HYDROGENATION CATALYST, AT A PRESSURE OF FROM ABOUT 150 P.S.I.G. TO ABOUT 300 P.S.I.G. AND AT A TEMPERATURE OF FROM ABOUT 450* F. TO ABOUT 700* F., BUT BELOW THE TEMPERATURE AT WHICH APPRECIABLE DEHYDROGENATION OF NAPHTHENES TO AROMATICS OR HYDROCRACKING WILL TAKE PLACE AT THE PRESSURE USED, ANS RECOVERING AN OIL WHICH WILL NOT DISCOLOR ON HEATING TO A TEMPERATURE IN EXCESS OF 400* F. 